Cover photograph (Copyright © 2003, American Society for Microbiology. All Rights Reserved.): Biofilm colony of Actinobacillus actinomycetemcomitans growing attached to the surface of a polystyrene petri dish containing broth medium. The growing colony releases cells into the medium, and the released cells attach to the surface of the petri dish and form new colonies, enabling the biofilm to spread. The bacteria were stained with crystal violet. The imaged area is approximately 3 by 4 mm. (See related article on page 4693.)